The general processes employed in the prior art for the preparation of ethers include the dehydration of alcohols, the addition of primary alcohols to alkenes, and reaction between an alkyl halide and a sodium alkoxide or sodium phenoxide (Williamson synthesis). Dehydration of alcohols with acidic catalysts produces ethers by intermolecular dehydration and olefins by intramolecular dehydration. Dehydration of mixed alcohols, it is known in the art, produces mixtures of all possible ethers with no particular selectivity. For secondary alcohols, acid catalyzed dehydration using classical acids such as sulfuric acid can proceed to form a symmetrical di-secondary alkyl ether of the starting secondary alcohol, an olefin, water, and an isomer of the starting secondary alcohol by olefin isomerization followed by hydration.
In view of the multiplicity of possible reaction pathways, the acid catalyzed preparation of symmetrical di-alkyl ethers from secondary alcohols is known to proceed in the prior art with very low selectivity. Further, with increasing alcohol carbon number, i.e., C.sub.4 ', classical acid catalyzed dehydration of secondary alcohols in the prior art proceeds ever more preferentially toward intramolecular dehydration to form olefins with an ever decreasing selectivity for the formation of the symmetrical di-secondary alkyl ether of the starting secondary alcohol. Primary literature references substantiate the poor ether selectivity obtained by acid catalyzed reaction of secondary alcohols (N. L. Drake and F. P. Veitch, The Action of Sulfuric Acid on Butanol-2, JACS, 57, 2623, 1935 and Patai, The Chemistry of the Ether Linkage, Interscience Publishers, NY, 1967, p.458).
It has come to pass that ethers are receiving renewed attention as components of gasoline blends, stimulated in part by the goals of the 1990 Clean Air Act. The dominant approach is to combine methanol with isobutylene or isoamylene to produce methyl tertiary butyl (MTBE) and tertiary amyl methyl ether (TAME) for gasoline blends. However, the petroleum feedstreams rich in tertiary olefins for MTBE or TAME synthesis are also rich in linear olefins. Upgrading these linear olefins to more economically valuable components such as secondary ethers to be employed, inter alia, as gasoline blending components would significantly improve overall process economics. It is known that these linear olefins can be converted to secondary alcohols by hydration. Conversion of the secondary alcohols to ethers, particularly symmetrical di-secondary alkyl ethers at high selectivity, would fulfill the need to maximize the utilization of linear olefins for ether production and provide a means to economically manufacture symmetrical di-secondary alkyl ethers not readily available by others processes.
Accordingly, it is an objective of the present invention to provide a process for the production of symmetrical di-secondary alkyl ethers from secondary alcohols.
It is a further objective of the present invention to provide a process for the production of symmetrical di-secondary alkyl ethers from secondary alcohols with high selectivity employing acid metallosilicate particles as catalyst.